hi everyone, i have been doing research that needs to measure the specific surface area(SSA) of the sample. However, after i measured the same sample 3 times, there is an error between the results(18,20,28m2/g respectively).
Unfortunately, what i will do is to compare the ssa of three types of particle , the differences between which are slight. I use ~100mg of my sample to measure each time. So, i just want to know how accuracy the BET result can be according to your experience?
Thank you.
regards.
See the references: http://sol.rutgers.edu/~aneimark/PDFs/IUPAC_Report_PAC_2015.pdf https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4523471/
Usually, to have a good precision on the measurement of the BET surface area, you should have at least 20 m2 in the measurement cell. In your case, you should then have 1g of material.
Good questrion. I am also intetrested to know the number of replications needed for bET measurement. Generally statistian recommed three replications.
Depending on the setup in your lab, I would say that sample weighing is the largest source of error. In my previous job I had a lot of problems with precision when weighing ~200 mg samples. I would recommend weighing the sample alone, then transferring it to a BET tube of known weight and double checking the net weight.
It sounds as if you have too little sample. Also you have not stated your outgassing regime. For samples that have already been heat treated to 500°C or higher I always out gas overnight at 300°C. Even with a non-microporous alumina I found that out gassing at 140°C was insufficient to achieve consistent reproducible results.
Best regards,
Malcolm
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